High free-acid iron phosphate conversion coating composition and method

ABSTRACT

A CONVERSION COATING COMPOSITION FOR FERROUS AND NONFERROUS METAL SURFACES EMPLOYING A PHOSPHATE COMPOSITION IS IMPROVED BY THE INCORPORATION OF ETHYLENE DIAMINE TETRA ACETATES. AN AQUEOUS BATH, HAVING A RELATIVELY HIGH FREE ACID CONTENT, IS MADE POSSIBLE BY THE EMPLOYMENT OF ETHYLENE DIAMINE TETRA ACETIC ACID AND/OR ITS SALTS. THE FREE ACID TO TOTAL ACID RATIO BECOMES FUNCTIONAL EVEN AT A RATIO AS HIGH AS ONE TO TWO, TO PROMOTE THE ACTIVITY AND ACCELERATE THE FORMATION OF UNIFORM IRON PHOSPHATE CONVERSION COATINGS HAVING A HIGH DEGREE OF HARDNESS, ADHERENCE AND TENACITY TO THE METAL BASE.

United States Patent 3,579,389 HIGH FREE-ACID IRON PHOSPHATE CONVER- SION COATING COMPOSITION AND METHOD George D. Howell, Alton, Ill., and Robert F. Ayres, Florissant, Mo., assignors to Electrolux Corporation, New York, N.Y. No Drawing. Filed Oct. 31, 1967, Ser. No. 679,555 Int. Cl. C23f 7/08 US. Cl. 1486.15 13 'Claims ABSTRACT OF THE DISCLOSURE A conversion coating composition for ferrous and nonferrous metal surfaces employing a phosphate composition is improved by the incorporation of ethylene diamine tetra acetates. An aqueous bath, having a relatively high free acid content, is made possible by the employment of ethylene diamine tetra acetic acid and/or its salts. The free acid to total acid ratio becomes functional even at a ratio as high as one to two, to promote the activity and accelerate the formation of uniform iron phosphate conversion coatings having a high degree of hardness, adherence and tenacity to the metal base.

BACKGROUND OF THE INVENTION Processes for beneficiating the surface of a metal which is generally to be fabricated and painted, known as iron phosphate coatings, have been in use for many years.

The general principles behind these processes involve the change, or conversion, of the surface layers of a metal from their normal state into a salt or compound of that metal. This conversion of the outermost atoms of the metal lattices, when properly accomplished, can result in the imparting of corrosion-resistant properties to the surface. This type of surface change, to form a thermodynamically stable precipitate which is integrated with the surface, and bound to it by molecular forces, is relatively old in the art.

Normally, the first basic principle involved in metal surface conversion lies in subjecting the metal part to be coated to a solution containing acid anions, which then form insoluble products when they react with the metal at the interface between metal surface and solution. The acidity of the solution is adjusted so that the reaction between metal and acid anion just neutralizes the acidity; i.e., raises the pH, at the interface, to the extent that insoluble metal compounds are formed at and with the metal surface. The insoluble products thus are integrated with the metal. The acid anion commonly and most effectively used is the anion of primary phosphates; namely, H PO In iron phosphating the sources of such anions are generally from solutions of the primary alkali metal phosphates and from primary ammonium phosphates. However, they may be supplied also from soluble metal phosphates such as calcium, zinc and iron. Solutions are thus likely to be based on NaH PO KH PO NH H PO or sometimes from Ca(H PO were).

and Fe(H PO organic complexer organomolybdenum complex 3,579,389 Patented May 18, 1971 A solution of salts mentioned above, however, will not in itself provide the continuous, non-porous, uniform reaction with the metal surfaces which are required by modern industrial processes. Such solutions must be and usually are modified in some way or another. Generally, phosphate coatings may be characterized under two broad classifications: (l) amorphous conversion coatings, and (2) crystalline conversion coatings. The iron phosphate coatings are usually of the amorphous structure.

In order to phosphate a metal surface, the surface must first be thoroughly cleaned. In the case of the heavy crystalline or microcrystalline coatings (usually referred to in the trade as zinc phosphating), the cleaning is accomplished in a separate step prior to the application of the phosphating solutions. This separate step is necessitated because the zinc phosphating solutions are difficult to apply with surface active agents in the same bath, mostly because of incompatibility between the surface active agents and free acid and/or heavy metal ions. On the other hand, in common practice, iron phosphating solutions are applied with essentially no free acid and usually with low content of heavy metal cations. This lack of free acid is an advantage only with respect to allowing the use of synthetic detergents in the iron phosphating baths, which permits the same solution to be used as a metal cleaner as well as a conversion coating treatment. In most cases, iron phosphating baths do not require precleaning of the metal prior to application of the iron phosphating function.

The lack of free acidity is a disadvantage, however, with respect to increasing the activity, accelerating and improving the uniformity of iron phosphate coatings. There is a further disadvantage in that lack of free acid slows the bath and frequently results in longer time requirements for the coating reaction which may delay production lines cycles.

The incorporation of free acid into iron phosphating solutions to any appreciable degree has been avoided in the past because over-pickling and over-phosphating will generally result. Free acid in the iron phosphating solution will tend to attack the metal surfaces at relatively wide-spread, susceptible areas on the surface, rather than in uniform homogeneous fashion; the result is spotting and/or smutty coating action. This is of little value for improving the corrosion resistance and adhesion characteristics of the surface.

There is a further complication which renders the incorporation of free acidity into iron phosphating systems even more inimical for the performance of proper conversion coating function. This complication arises from the fact that a properly constituted iron phosphating material will contain certain accelerating components which are necessary for the rapid formation, adhesion, uniformity, hardness and corrosion resistance of the coatmg.

Accelerating agents that are frequently used in practice include compounds of such metals as vanadium, titanium, zirconium, tungsten and molybdenum. The compounds utilized most fresuently are the molybdates. An illustration of the manner in which the molybdate ion, M005, functions as an accelerating and supplementary coating ingredient from an organic complex is as follows:

M004= acid phosphate steel surface small equilibrium concentrations of soluble molyb date Unless there is a modification such that the molybdate is incorporated into some kind of a complex molecule, where it is fed out to the metal surface in proper minute amounts, it will appear on the surface of the metal only as a smutty deposit. In other words, the mo lybdate cannot be used per se, as it tends to form spongy, porous coatings which are of no value. This deleterious effect is especially pronounced in the presence of excess free acidity. The molybdate has heretofore in practice been utilized by complexing it with certain organic molecules; examples are sugars, polyhydroxy phenols, tannins, etc. These organic complexes of molybdenum perform more or less efiiciently in feeding out molybdic oxides which are then integrated into the iron phosphate precipitates under proper equilibrium conditions. In other words, the molybdenum accelerating reaction can yield suitable, hard, uniform, evenly-colored coatings in the presence of the agents mentioned above. Before this invention, this was true only if there was no substantial free acid content in the phosphating bath.

SUMMARY OF THE INVENTION By means of this invention there has been provided a composition for producing an iron phosphating bath which will incorporate the rapid action to be obtained from free phosphoric acid, but avoid overpickling and overphosphating, and at the same time allow the use of surface active agents in the composition of the bath. The composition produces a unique and novel fast-acting highly efiicient metal cleaning and coating bath having a properly balanced percentage of active ingredients, which is of great value to the metal fabricating industries.

By the use of free acid, relatively high in its ratio to the total acid content in the iron phosphating composition, stabilization of much more highly concentrated liquid products is obtainable than heretofore possible. Thus, considerably higher active concentrations may be held in solution without settling or sludging out, and the makeup of a working bath is readily and simply accomplished.

Primarily, the invention consists of utilizing the stable complex formed between ethylene diamine tetra acetate and molybdic acid to produce a phosphate coating accelerator of superior qualities. The ethylene diamine tetra acetate and molybdate complex prevents formation of smutty, spongy coatings by controlling overphosphating and by causing insoluble molybdic oxides to form the coating at a controlled and desirable rate.

In the composition, the molybdenum feeds from the complex under equilibrium conditions to give tightness and adherence of the coating with uniformity in color and homogeneity of surface conversion. The complex yields molybdenum ions at a minute and controlled rate, and thus preserves the reservoir of this expensive accelerating agent without loss of stability.

The ethylene diamine tetra acetate and molybdic complex is not subject to premature oxidation-reduction since it may be maintained separate from the final solution until used, and thus can be kept in a stable condition retaining higher oxidation states of molybdenum which are subsequently available for reduction at the metal surface. Through this controlled formation of the ethylene diamine tetra acetate and molybdic complex, there is no deep color change associated with aging and storage. In contrast, sugar or tannin molybdic complexes degrade to deep green or blue colors, indicating premature molybdenum reduction, and decreased accelerating efiiciency in other iron phosphate conversion coating compositions. This effect is avoided by the instant invention.

The stability of the ethylene diamine tetra acetate and molybdic complex is such that free acid may be used in the iron phosphating baths prepared through the use of the composition of this invention. This permits faster and more homogeneous reaction rates. The complex prevents 4 over-pickling and over-phosphating even in the presence of a free acid to total acid ratio as high as one to two.

The ethylene diamine tetra acetate component acts synergistically with other commonly used organic complexing agents, such as sugars, tannins, polyhydroxy phenols, starches, and the like, and serves to retard their oxidation by the molybdates. The ethylene diamine tetra acetate complex can also provide improved results when combined with other metal accelerators than the molybdates. Such accelerators are sometimes used in iron phosphate coating compositions and the ethylene diamine tetra acetate effectively modifies and complexes accelerator compounds employing tungsten, titanium, zirconium, cobalt, nickel and vanadium. The ethylene diamine tetra acetate is unique in the composition of this invention among the other common chelating agents, in that it resists oxidation and promotes improvements in surface conversion coatings.

The above features are objects of this invention and further objects will appear in the detailed description which follows and will be otherwise apparent to those Skilled in the art.

DISCLOSURE The beneficial attributes of the iron phosphating solution of this invention are accomplished by the use of certain chelating molecules. Of particular benefit and of very practical use is ethylene diamine tetra acetate acid, known as EDTA, and its salts. The EDTA apparently forms a complex with the soluble molybdenums component which, even in the presence of excess acid permits it to feed out in reduced and insoluble form on the metal surface. It appears that the complex formed in a weakly acid solution has the exact stability product constant most suitable for using molybdenum to accelerate coating formation.

In order not to restrict this invention solely to the use of molybdenum type accelerators, it should be noted that the EDTA complex functions similarly in vanadium compounds. The accelerating effects may also be accomplished from the complex of EDTA and compounds of Ti, Zr, Co, W, and Ni. For the coating composition of this invention, the molybdenum is preferred as it provides superior color and uniformity of surface.

As an additional desirable and novel aspect of this invention we have found that the presence of soluble EDTA compounds improves synergistically the action of organic modifiers described before. Namely, the presence of EDTA with sugars, tannins, polyhydroxy phenols, etc., produces a coating action with molybdate, and other metal accelerators, which is superior to a single organic complexing ingredient alone.

A very important additional aspect provided by this invention, stems from its ability to preserve the molybdenum ion in its highest oxidation state. Obviously, if it is desirable to reduce molybdate to a lower, insoluble oxide which is subsequently incorporated in sito into the conversion coating itself, it is necessary to prevent the reduction of the molybdate ahead of time, before it can react with the metal surface. Of additional value in such a procedure; i.e., maintaining MoO in an oxidized state, is the fact that the molybdate should enter into a redox reaction in which the ferrous ion is oxidized to ferric, so that the iron precipitate at the metal surface develops into the more insoluble ferric salt. The following equation may serve to illustrate the development of one kind of a mixed, insoluble conversion reaction, occasioned by the simultaneous reduction of MoO to say, M0 0 and the oxidation of Fe++ to Fe+++ in the presence of P0 It may be derived that the M00 also serves as oxidant to convert any nascent hydrogen gas, evolved from the pickling action, into water.

As an illustration of the degradation which the molybdenum accelerator may undergo in phosphating powders or solutions which have been extant prior to this invention, it is found that the products show a change in coloration on aging. The development of this blue or green color even before the products are used, graphically demonstrates the change of MoO to a lower oxide. The lower molybdenum oxides are usually blue or green. The development of the color in the product prior to its actual application to metal means that insoluble oxides of molybdenums have formed and are no longer available to act as oxidizing agents in the solution nor are they capable of plating out in desirable form as an integral part of the conversion coating.

If the molybdate is thus reduced prior to application to the metal, the result is decreased coating weights, poorer colors on the surface, less effective corrosion resistance and loss of adhesion properties for organic finishes.

The iron phosphate coating contains preferably a molybdenum compound as an accelerating metal ingredient.

Compounds of molybdenum promote the phosphate action on the surface of metals and act by seeding or plating out on the surface, and then incorporating themselves as lower oxides of molybdenum with the iron phosphate precipitate which forms in the reaction. In some ways they plate out in a manner similar to copper from an acid cupric solution which is exposed to steel. However, the molybdenum comes out in the form of oxides rather than the metal, and leads to a supplementary protective noncorrosive coating, whereas copper will form a galvanic couple which leads to excessive corrosion. Although applicants do not wish to be bound by theory, it is proposed that the chemical plating or precipitating or coating reaction is as follows:

DERIVATION OF EQUATION Molybdenum compounds are introduced into the liquid iron phosphating composition in the form of molybdic acid, or a soluble molybdenum complex giving forth to MoO ion. When the molybdenum exists solely as uncomplexed molybdate ions in an acid phosphate solution, and ferrous metal parts are then introduced into this solution, the molybdate will tend to plate out, as described above, but may very well come out in a soft, smutty deposit which is of no value whatsoever, and, in fact, is detrimental to subsequent operations on the metal surface, such as painting. By means of the employment of ethylene diamine tetra acetic acid and its salts, as disclosed in this invention, such soft smutty coating is avoided through controlled release of the molybdenum.

In this invention the molybdate acceleration is promoted without the smutty deposit by insuring that the conversion coating is quite thin, homogeneous, finegrained, and integrated properly in proper ratio with the ferric iron phosphates which lay down at the same time as the molybdic oxides from the acid phosphate bath. The ethylene diamine tetra acetic acid used as a chelating agent to control the release of the molybdenum and improve greatly its accelerating effects is unique in this invention. The molybdenum, through the use and employment of ethylene diamine tetra acetic acid, performs to release the molybdenum slowly in an equilibrium way from the bath to the metal surface in conjunction and completely integrated with the iron phosphate coating itself.

One of the major reasons why EDTA seems to function in a much more efficient fashion than do the other chelating types seems to result from its resistance to oxidation by molybdate. Molybdenum is in the same family in the Periodic Table as chromium and therefore, it can form oxidizing agents, although somewhat weaker in character than the corresponding chromates. Nevertheless, under the proper conditions molybdates do oxidize certain organic materials, including such phosphate coating modifiers as the commonly-used tannins and sugars. It also oxidizes most other organic chelating agents, as evidenced by the fact that, with such chelaters, the entire body of the powdered or liquid iron phosphate coating material will turn green or blue long before it is ever put to use in the solution tank. No such color change develops between molybdates and EDTA; hence, redox reactions do not prematurely occur.

Of course, the very fact that the molybdate is not acting as an oxidizing agent on the EDTA also implies that it does not itself become reduced to its lower oxides in advance of the time when it is desirable to use it as an accelerating agent. Obviously, if before use, the molybdate has already assumed a lower oxide form, say from Mo0 or M00 down to an oxide such as M0 0 the availability of molybdenum for accelerating the coating action has been largely lost. Many commercial products will in the course of a few days or a few weeks turn completely blue or dark green, indicating reduction of molybdate. The novel finding of this invention concerned with the EDTA salt is the fact that molybdate maintains its integrity in color. It retains its white or yellow color in the complexed concentrated solution.

Usage of the Mo-EDTA complexes is actually more important, from the practical standpoint, in additive or booster solutions than anywhere else, as far as liquids are concerned. Such boosters containing MoO without EDTA may turn blue or green. They do not do so when EDTA is present. The pre-reduced molybdate does not function as well in the bath as it would have from a higher oxidation state. Of course, the molybdate reduction is desirable and necessary at the instant of coating reaction, when at solution and metal surface interface incipient reactions start. At this point, pickling action produces ferrous ion, which in turn reduces molybdate, and the iron is itself oxidized to ferric ion, in situ. The ferric precipitate forms a more insoluble phosphate and the molybdic oxides combine with it to yield a strong spinel-like reaction product at the surface (with the surface, or even in the surface), bonded with the metal by molecular forces and possessing good color and uniformity. The coating shows no tendency to wipe-off, as it might with many of the other accelerators. Thus overphosphating and overpickling is eliminated by the use of the complex of this invention.

In the preparation of the phosphate coating composition, two solutions are employed in the make-up of the bath. The first solution is termed a concentrated phosphate solution, while the second is a concentrated additive solution that is termed a booster. The phosphate solution has a high proportion of free acidity, up to one-half of the total acid content. The product may be buffered with respect to pH changes and also contains the molybdate accelerator which enters into the coating reaction. The additive or booster solution contains the ethylene diamine tetra acetate complexing agent and additional molybdate for replenishing accelerator in the final composition bath. Desirably, sugar modifiers and a high concentration non-ionic and/or amphoteric synthetic detergents may also be employed in the booster solution.

For the purpose of example, there are listed below liquid phosphating baths made according to this invention.

EXAMPLE 1 Wt. percent Range H PO4. anhydrous basis 15 -56 Molybdic acid 0. 25 0. l-2 Ethylene diaminc tetra acetate 1 3 0. 5-10 Water 81. 75

Total 100. O0

1 Versene tetra sodium salt from Dow Chemical Company.

or a ratio of free acid to total acid of one to two.

Examples 2 through 7 below represent examples using accelerators using compounds of vanadium, zirconium, tungsten, cobalt, nickel and titanium.

EXAMPLE 2 Phosphate solution: Wt. percent H PO anhydrous basis 35.0 NaH PO 20.0 NH VO 1.0 Water 44.0

Booster solution:

Catechol 5.0

Na EDTA 5.0 Non-ionic or amphoteric surfactants 25.0 Water 65.0

EXAMPLE 3 Phosphate solution: Wt. percent H PO anhydrous basis 20.0 KH PO 40.0 ZrO 'XH O 1.5 Water 38.5

100.0 Booster solution:

Na EDTA 2.0 Zl'OgXHzO Non-ionic or amphoteric surfactants 40.0 Water 57.5

EXAMPLE 4 Phosphate solution: Wt. percent H PO anhydrous basis 37.0 NH H PO 10.0 Ni(NO '6H O 2.0 Water 51.0

8 Booster solution:

Glycerol 15.0 Na EDTA 10.0 Ni(NO 6H O 0.5 Non-ionic surfactants 30.0

Water 44.5

100.0 EXAMPLE 5 Phosphate solution: Wt. percent H PO anhydrous basis 67.0 C3-(H2PO4)2 Na WO Water 28.7

100.0 Booster solution:

Quebracho tannin 3.0 K EDTA 1.0 Na WO 0-5 Amphoteric surfactants 20.0 Water 75.5

100.0 EXAMPLE 6 Phosphate solution: Wt. percent H PO anhydrous basis 70.0 ZH(H2PO4)2 TiO 1.0 Water 26.5

100.0 Booster solution:

Pyrogallol 2.0 Na EDTA 2.0 Ti (C O 10H O 4.0 Non-ionic surfactants 40.0 Water 52.0

100.0 EXAMPLE 7 Phosphate solution: Wt. percent H PO anhydrous basis 50.0 Mg(H PO Co(NO 7H O 2.2 Water 37.8

100.0 Booster solution:

Mannose 5.0 Na EDTA 6.0 Co(NO 7H O 3.0 Non-ionic and amphoteric surfactants 27.0 Water 59 0 100.0 EXAMPLE 8A Phosphate solution: Wt. percent H PO anhydrous basis 23.00 NaH PO anhydrous basis 55.00 Molybdic acid M00 0.25 Water 21.75

100.00 Booster solution:

Sugar 2.0 Molybdic acid (85% M00 0.5 Ethylene diamine tetra acetate (Versenc sodium salt from Dow Chemical Co.) 4.0 Non-ionic or amphoteric surfactants 32.0 Water 61.5

In this example the surfactants may be blended in desired ratios to present various properties forming no part of this invention per se. A typical blend in the booster solution of Example 8A for use in immersion tanks is 10-15% of a non-ionic alcohol ethylene oxide adduct such as Surfonic LRlSO of Jefferson Chemical Co., and 17-22% of an amphoteric disodium N-tallow B-amino dipropionate such as Deriphat 154 of General Mills, Inc. A typical booster solution blend for spray coating use is 19% Deriphat 154 and 13% Surfonic LR150.

In a typical use the phosphate solution and booster solution of Example 8A are each mixed together in water to provide 0.50% by volume of each of the solutions in the bath. The ranges of the components in the finally prepared complete phosphate coating solution are shown as follows in Example 8B.

EXAMPLE 813 Percent by weight Free acid, calculated as P 0.1-2.25 Fixed acid, calculated as P 0 0.04.05 Total acid, calculated as P 0 0.1-4.50 Free acid/ total acid ratio 0.1-0.50 Molybdates, calculated as M00 0004-0055 Sugar 0005-0102 EDTA 0005-050 Non-ionic surfactants 0.09-1.98 Water, q.s.

In making up the liquid bath, the phosphate concentrate is customarily dissolved in water in a concentration range between 0.25 and 3% by volume. The concentrated additive or booster is added to the same solution at a concentration range between 0.25 to 5% by volume. The two diiferent solutions are employed in the final liquid bath and may be added for make-up as the solution is used up. Thus, in the liquid phosphate solution, the phosphate, acid strength, and accelerators are provided through one concentrated liquid, while in the additive or booster solution molybdate replenishing materials are employed, together with the organic complexers and the ethylene diamine tetra acetate in highly concentrated form.

In the examples the free acid exists as H PO which is titratable to Brom Cresol Green Indicator. The fixed acids are represented by primary sodium, potassium, or ammonium orthophosphates, but it will be understood that there may also be incorporated primary calcium, magnesium, iron or zinc orthophosphates. This acidity is titratable from the Brom Cresol Green endpoint to the Oleo Red B endpoint. The molybdates employed may be molybdic anhydride, molybdic acid, ammonium molybdate or sodium molybdate. It will further be understood that the organic complexer, sugar, may be omitted from the bath, or substituted as described above by other organic complexers such as tannins, dextrose, starches, glycols, or polyhydroxy phenols.

Various changes and modifications may be made within this invention as will be readily apparent to those skilled in the art. Such changes or substitutions are within the scope and teaching of this invention as defined by the claims appended hereto.

What is claimed is:

1. A metal cleaning and surface coating composition having a high free acid to total acid ratio consisting essentially of an aqueous solution of free phosphoric acid, a fixed acid from at least one member of the group con- 10 sisting of primary orthophosphates of sodium, potassium, ammonium, calcium, magnesium, iron and zinc, an accelerator of at least one member of the group consisting of a compound of molybdenum and vanadium and ethylene diamine tetra acetic acid.

2. The composition of claim 1 in which dextrose is added.

3. The composition of claim 1 in which at least one member of the group consisting of non-ionic and amphoteric surface active agents are added.

4. The composition of claim 1 in which the accelerator is a compound of molybdenum.

5. The composition of claim 1 in which the accelerator is a compound of vanadium.

6. The composition of claim 1 is which there are added dextrose, and at least one member of the group consisting of non-ionic and amphoteric surface active agent.

7. A method for phosphate coating metals to provide a protective coating comprising treating a metal surface to be coated with a liquid coating composition, preparing said liquid coating composition in the form of a phosphate solution and a booster solution, said phosphate solution having a high free acid to total acid ratio and containing free phosphoric acid in aqueous solution and a fixed acid from at least one member of the group consisting of primary orthophosphates of sodium, potassium, ammonium, calcium, magnesium, iron and zinc, said booster solution containing a relatively concentrated aqueous solute of an accelerator of at least one member of the group consisting of a compound of molybdenum and vanadium and ethylene diamine tetra acetic acid, mixing the phosphate solution and the booster solution and applying the liquid coating composition to the surface of the metal to be treated.

8. The method of claim 7 in which the accelerator is a compound of molybdenum.

9. The method of claim 7 in which the accelerator is a compound of vanadium.

10. The method of claim 7 in which a fixed phosphate acid is added.

11. The method of claim 10 in which there are added to the booster solution dextrose and at least one member of the group consisting of non-ionic and amphoteric surface active agents.

12. The method of claim 7 in which dextrose is added to the booster solution.

13. The method of claim 7 in which at least one member of the group consisting of non-ionic and amphoteric surface active agents is added to the booster solution.

References Cited UNITED STATES PATENTS 2,462,196 2/1949 Jernstedt l486.15 2,502,441 4/1950 Dodd et al. l486.15 2,743,204 4/ 1956 Russell l486.15 2,758,949 8/1956 Ley et al. 1486.l5 2,854,369 9/1958 Kronstein 148-6.15 3,268,367 8/1966 Nelson l486.15 3,269,877 8/1966 Schlossberg 1486.15 3,294,593 12/1966 Wyszomirski 148-6.15

OTHER REFERENCES Sathyanandham et al., Metal Finishing, August 1967, pp. 48-51.

The Chemical Age, Sept. 1, 1951, pp. 295, 296, 300.

RALPH S. KENDALL, Primary Examiner 

